Conventionally, an image reading apparatus is provided in a copying machine or the like. In some image reading apparatuses, originals supplied from an auto document feeder can be read by a scanner unit stopped at a predetermined position, while conveyed in a sub-scanning direction. An image reading apparatus capable of reading both sides of an original is also known (refer to Japanese Laid-open Patent Publication No. 2003-008836, for example).
With reference to FIG. 32, an explanation will be given of an image forming apparatus equipped with an image reading apparatus capable of reading both sides of an original. FIG. 32 is a longitudinal section view showing the construction of an image forming apparatus having a conventional image reading apparatus.
As shown in FIG. 32, the image forming apparatus includes an image reading apparatus A that reads image information on an original, and a printer apparatus B that forms an image on a sheet based on the image information read by the image reading apparatus A.
The image reading apparatus A is comprised of an auto document feeder (hereinafter referred to as the ADF) and a scanner apparatus 1. The ADF 2 includes an original tray 12, a pickup roller 43, a pair of separation rollers 44a, 44b, a plurality of conveyance rollers 46, 48, a discharge roller 49, and a discharge tray 50. Originals D are stacked on the original tray 12. The originals D stacked on the original tray 12 are separated one by one by the pickup roller 43 and the separation roller pair 44a, 44b, and then delivered to a conveying path 156. Each original D is conveyed by the conveyance roller 46 along the conveying path 156, and an image on the original D is read by the scanner apparatus 1. After the image reading, the original is discharged to the discharge tray 50 by the conveyance roller 48 and the discharge roller 49.
For double-sided reading of originals D, there is provided an inversion flap 152 at a location downstream of the conveyance roller 48. Also provided is an inversion conveying path 153 that inverts a surface of the original D being scanned.
The scanner apparatus 1 has a platen glass 22 and a scanner unit 21 disposed below the platen glass 22. The scanner unit 21 is constructed so as to be movable in a direction shown by an arrow F in FIG. 32 (sub-scanning direction), while being guided by a guide rail 24. The scanner unit 21 is equipped with a plurality of lamps 21c that irradiate an original, a line CCD (charge coupled device) 21g, an optical system 21f that guides light reflected from the original irradiated by the lamps 21.
The image reading apparatus A has two scanning modes, i.e., an original flow scanning mode and a fixed original scanning mode, and is capable of reading an original in each of these scanning modes.
The original flow scanning mode is a mode where an original fed from the ADF 2 is read by the scanner unit 21 while being conveyed in the sub-scanning direction. Specifically, an original D is fed from the ADF 2, and the original D is conveyed in the sub-scanning direction. At this time, the scanner unit 21 is caused to stop at a flow reading position 101. When the original D conveyed in the sub-scanning direction passes through the flow reading position 101 while being in close contact with a flow scanning glass 102, the scanner unit 21 reads the original D in a main scanning direction. As a result, the entire one side of the original D is read. Then, the original is discharged to the discharge tray 50 by the conveyance roller 48 and the discharge roller 59. In this manner, the one side of the original D is read.
When a double-sided scanning mode is selected in the original flow scanning mode, the original D is pulled out by the discharge roller 49 until its rear end passes through the inversion flap 152 after a first side of the original D has been read. The inversion flap 152 is switched and the discharge roller 49 is reversely driven. As a result, the original D is introduced into the conveying path 153 and the surface of the original to be scanned is inverted. The original D is conveyed again by the conveyance roller 46 toward the flow reading position 101, and a second side of the original D is read by the scanner unit 21. In this manner, both the sides of the original D are read.
On the other hand, in the fixed original scanning mode, the original D is placed on the predetermined position on the platen glass 22, and the scanner unit 21 is moved in the sub-scanning direction relative to the placed original D. Specifically, the scanner unit 21 is moved in the sub-scanning direction relative to the original D placed on the platen glass 22, while reading the original D in the main scanning direction, whereby the entire original is read.
The printer apparatus B includes a laser unit 3. The laser unit 3 modulates laser light based on image data (video signal) read by the image reading apparatus A, and irradiates the laser light onto the photosensitive drum 10. As a result, an electrostatic latent image is formed on the photosensitive drum 10. The electrostatic latent image formed on the photosensitive drum 10 is visualized into a toner image by toner supplied from a developing unit 11. The toner image is transferred by a transfer unit 6 onto a sheet P fed from a sheet cassette 4 via a resist roller 5. The sheet P on which the toner image has been transferred is delivered to a fixing device 7. The fixing device 7 heats and presses the sheet P, thereby fixing the toner image on the sheet P. The sheet P on which the toner image has been fixed is discharged to a discharge tray 9 by a discharge roller 8.
However, in the original flow scanning, when the flow scanning glass 102 has a stain, such stain can produce image streaks extending in the sub-scanning direction in the read image information. For example, an original is sometimes stained with ballpoint ink, correction fluid, glue or the like. When such stain is adhered to the flow scanning glass during the original reading process, image streaks are produced in subsequently read image information. These image streaks cannot be eliminated unless the stain on the flow scanning glass 102 is removed, making it impossible to obtain an image of high quality.
Recently, an image reading apparatus has been in practical use, in which two image reading devices are disposed on both sides of an original conveying path, and images on both sides of an original being conveyed along an original conveying path extending between these devices are simultaneously read the image reading devices.
With reference to FIG. 33, the above image reading apparatus will be explained. FIG. 33 is a longitudinal section view showing the conventional image reading apparatus capable of simultaneously reading images on both sides of an original.
As shown in FIG. 33, the image reading apparatus includes two scanner units 121, 160. The scanner unit 121, 160 are disposed at a flow reading position 101 so as to face each other, with a conveying path 161 interposed therebetween. Each of the scanner units 121, 160 is the same in construction as the scanner unit 21 of the aforementioned image forming apparatus.
In the image reading apparatus, originals D are delivered one by one from an original tray 12 to the flow reading position 101. When each original D passes through the flow reading position 101, an image of a first side of the original D is read by the scanner unit 121, and at the same time an image of a second side of the original D is read by the scanner unit 160. Thereafter, the original D is discharged to a discharge tray 50 by a conveyance roller 49.
The image reading apparatus having the construction shown in FIG. 33 is capable of reading both sides of an original in a short period of time, offering high productivity. However, as in the construction shown in FIG. 32, when either the scanner unit 121 or 160 has a stain at its face facing an original, the stain can produce image streaks extending in the sub-scanning direction in the read image information. It should be noted that, with the construction shown in FIG. 33, a deviation can occur between scanned images of the first and second sides of the original. D when the scanner unit 160 is not accurately positioned relative to the scanner unit 121, resulting in such drawbacks that the images are distorted. In particular, in a case where the scanner unit 121 is provided in the scanner apparatus 1 and the scanner unit 160 is provided in the ADF 2 that can be opened and closed relative to the scanner apparatus 1, an adjustment device must be provided for aligning the relative positions of the scanner units 121, 160.